Rectifier for motion picture projectors



Feb. 13, 1934. R. D. AMSDEN RECTIFIER FOR MOTION PICTURE PROJECTORSFiled oct. 12, -1952 Y 2 sheets-sheet 1 Inventor: Ralph D.Am5de,`

His Attorney.

Feb. 13, 1934. R. D. AMsDEN 1,947,240

RECTIFTER FOR MOTION PICTURE PROJECTORS Filed oct. 12, 1932 V2sheets-sheet 2 hmvewmtoxr` Ralph D. Amsden,

bk MT "J His Attovnerg.

Hurrah STATES PATENT OFFICE- anc'rrrma ron MorroN rrc'ruan Ralph n.

eral Electric Company,

York

PROJECTORS l Amsden, Lynn, Mass., assignor to` Gena corporation o! NewApplication. October 12, 1932. Serial No. 637,459 4 claims. (el.irs-sse) My Vinvention relates to current-rectifying apparatus of thedry rectifier type designed'to supply 'direct-current power fromalternating-- current lines for the operation of motion picture arclamps or the like, and its principal object is the provision of animproved apparatus arrangement and of an improved air-cooling means forthe rectifier apparatus, .whereby relatively high current outputs forthe arc lamps of high power motion picture projectors are obtained froma low-cost rectifying apparatus of the dry-rectifier type.

In the recent past a large number of rectifying apparatus have beenemployed to -supply direct curent from alternating-current means for thearc lamps of motion picture projectors in small or medium sizedtheatres. Such rectifying apparatus have been of relatively lowcapacity, for

example, 20 to 3() amperes, for operating the soca1ledlowintensityprojectors.-

While these equipments have been generally satisfactory, rapid changesin the motion picture art have occurred demanding changes in theprojector equipment. Color pictures, .wide lm, greaterscreen area, etc.,all require more light at the projector. lTo meet this demand theatreshave been and are changing from the abovementioned low-intensityprojectors, operating at 'an arc current of 20 to 30 amperes, to thehigh-intensity reflector type projector operat-` ing at an arc currentof 60 to 70 amperes. y

Difliculties have been encountered, however, in the attempt to develop acopper-oxide or similar dry rectier apparatus to supply the high outputrequired in this more recent service in which the high-intensityprojectors are employed.A

Particularly, difiiculties' have been encountered due to insuflicientmeans for dissipating the heat losses unavoidably present intheoperation ofthe rectifier elements required to supply the relativelyheavy current to the projectors, with convsequent overheating endfailure of the rectifier units.-

apparatus unit, force the air over the rectier elements and in contactwith `radiating fins of special form associated with these elements,`and thence out through-the upper portion of the unit.l Batlle elementsare so arranged with relation to 00 the rectifier elements and theblowers that the air blast is directed solely over the rectifierelements and the radiating fins associated therewith, and is maintainedout of contact with insulating and mounting members employed inconnecting therectifler elements to the frame or casingv of theapparatusunit, all of the air supplied from the blowers being, therefore, madeuse of tothe best advantage in dissipating the heat losses.

My invention vwill be better understood from the following descriptionwhen considered in connection with the accompanying drawings and itsscope will be pointed out in the appended claims.

Referring to the drawings, Fig. l is a perspective' 75 View of arectifying apparatus u nit in accordance with my invention, the'front ofthe casing member being broken away to show two rectifier units,together withblowers lmounted. therein; Fig. 2 is a top View on a largerscale of one of the rectifier units shown in Fig. 1; and Fig. 3 is abottom view on a larger scale of one of the rectifier units and y the'blowerassociated therewith, shown in Fig. l. In the perspective view ofFig. 1, the numeral 10 designates a rectfying apparatus comprising 85 acasing 11 open at the bottom for the ingress of air and in which aremounted, preferably horizontally, two rectifier units 12 each providedwith a' blower 13 whichis locatedbelow and may be connected directly tothe. corresponding rectier unit. The units 12 may be arranged inparallel by suitable switch connections (not shown) to supply a single60 or 'Z0 ampere projector, or each units 12 preferably each' comprise aplurality of rectifier assemblies 14 made up in the usual manner byclamping copper oxide or other active elements, together with lead orother conducting plates, on a bolt or rod l5. Each assembly 14 100comprises a plurality of radiating ilns 16. The composition of the dryrectifier elements forms no part of my present invention and need notlbe further described herein. The rectifier assemblies 14 comprised inone of the rectifier units 12 l05 are arranged in two sections 17, 18,the assemblies of each section 'being mounted side by side in. a shallowcasingmember 19to the side walls 2O of which the rectifier assembliesare fastened by means of the bolts 15 and nuts 21, 22. 110

The blowers, as shown in the bottom view of Fig. 3, comprise each anelectric motor 23 and a fan 24, each blower being so mounted, as bybrackets 25 attached to the bottom plate 26 of a shallow open-toppedcasing '19, that the fan is located relatively closely to the undersides of the corresponding rectifier assemblies 14;

It will be understood that the blowers 13 are so arranged that the airblast is drawn in at the bottom ofthe apparatus casing 11 and is forcedupwardly through the shallow open-topped casings 19 containing therectiiier assemblies 14 arranged each in the sections 17, 18, the blastfinally passing out of the main casing 11 through a suitable opening oropenings (not shown) in the upper portion thereof.

In order to direct the air blast solely over the active elements ofrectifier assemblies 14 and the radiating fins 16 forming part of theseassemblies,-

I provide baiile elements as plates 29 extending from closely adjacentthe lower edges of the outer ends of rectifier assemblies 14 to the sidewalls 2@ of the shallow casings, and plates 30 extending between thelower edges of the inner ends of the rectiiier assemblies constitutingthe 'sections 17 and 18 respectively. The spaceabove the fan 24 in eachrectifier unit 12 is thus open for the passage ofvthe air blast in theregion of the active elements and radiating fins of the rectifierassemblies, but is entirely closed in the region of the rectifierassembly mounting means comprising such elements as the clamping nuts22, spring and compression washers 27, and insulating washers 28.

It will be observed that the arrangement of the closely spaced rectifierassemblies 14 with respect to the fans and to the air baffling meanscompris-l ing the shallow casings 19 and the baille elements 29 and 30is such that all of the` air used for cool-` ing is directed over theactive elements of the rectier units and between the radiating ns whichdraw the heat from the rectifier discs, the bathing means which areprovided preventing the air 'from fiowing over the mounting `portions ofthe assemblies at the ends thereof, or, in general, from owing'anywhereexcept directly in contact with the ns and those portions of the unitson which the fins are mounted. Consequently, efiicient use is made ofall of the air which is forced through the apparatus by the fans.

The fins 16 are specially shaped, for example, fiattened at the sides,to permit the mounting of the rectifier assemblies 14 closely adjacenteach other. The fins are preferably substantially .050 inch in thicknesswhich I have found is the proper thickness to cause the cooling air toconduct away the heat in the quantities in which it is generated intherectifier discs. Radiating ns employed, particularly in copper-oxiderectifiers, previously to my present invention have been constructed ofmuch thinner sheet metal than .above specified; ll have found that whenfins of the thinner material were employed, after the rectier apparatuswas shut down and the fan stopped, a thermometer placed on the Afinsshowed a temperature rise of 8y to 10 degrees, showing that ns of suchcharacter were not de- 'sirable for use in connection with the largeout-- put rectifier apparatus to which my invention is directed. I havefound that when radiating fins of substantially .050 inch thickness areemployed, the temperature will rise only from 1 to 2 degrees, showingthatl heat is conducted away from the active rectifier elements as fastas it is generated therein, and that the rectifier discs are kept ascool in operation as they should be kept in order to give satisfactoryaging characteristics.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. A rectifying apparatus for supplying direct current to high intensityarc projectors and the like comprising a rectifier um't including aplurality of rectifier assemblies of the dry disc type mounted closelyadjacent one another, each of said assembliesincluding a plurality ofactive elements and heat radiating fins, blower means adapted to supplycooling air to said unit, and means to cause the cooling air in passingthrough said rectifier unit to flow only over that portion of eachassembly including said active elements and said fins.

2. A rectifying apparatus for supplying direct current to high intensityarc projectors and the like comprising an apparatus casing, a pluralityof rectifier units mounted therein, each of said units including aplurality of rectifier assemblies of the dry disc type mounted side byside closely adjacent' in substantially the same plane, each of saidassemblies including a plurality of active elements and heatradiatingfins, a plurality of blowers each connected below a differentone of said rectifierl units to cause air to ow through said casing incontact with said units, and bafemeans assocated with said units tocause the air blast from said blowers in passing through said rectifierunits to flow only over said active elements and said fins. l

3. A rectifying apparatus for supplying direct current to high intensityarc projectors and the like comprising a rectifier unit including aplurality of rectifier assemblies of the drydlsc type, each of saidassemblies including a plurality of active elements and heat radiatingfins, a rela- 1 tively shallow casing member, means to mount 'saidassemblies closely adjacent each other in said casing, 'a blower mountedadjacent said casing to force air over said assemblies, and baille meansassociated with said casing to cause said air in passing through saidassemblies to iiow only over said active elements-andsaid fins.

4. A rectifying apparatus for supplying direct current to high-intensityarc projectors and the like comprising a rectifier unit including aplu-` rality of rectiiier assemblies of the dry disc type, saidassemblies being arranged side by side and closely adjacent in the sameplane, each of said 'assemblies including a plurality of active ele--I'ments and heat radiating fins, the thickness of '.said fins beingsubstantially .050 inch, blower 4means associated with said unit toforce cooling air therethrough, and means to cause said cooling aix' inpassing through said unit to fiow only over said active elements andsaid radiating tins.

RALPH D. AMSDEN.

